Serum and tissue concentrations of magnesium, calcium, potassium and sodium in rats

The aim of the study was to analyze concentrations of magnesium in the serum and selected tissues of Wistar rats (erythrocyte, myocardium, rectus abdominis muscle, femoral bone, lung, spleen, small intestine, liver, kidney and uterus in females) and to evaluate the relationships between serum and tissue concentrations of magnesium, calcium, potassium and sodium. Adult laboratory rats (Wistar strain, n = 39) were studied. The animals were allocated to three groups as follows: females (F; n = 18; bodymass, 269 +/- 33 g), males I (M I; n = 10; 413 +/- 30 g) and males 11 (M 11; n = 11; 633 78 g). The females and males were of the same age (10 - 12 weeks), the males 11 were older (22 - 24 weeks). Blood was drawn by cardiac puncture under ether anesthesia. After sacrificing the animals under ether anesthesia, tissue samples were collected from the tissues to be studied and analysed for the presence of magnesium, calcium, potassium and sodium. Flame atomic absorption spectrophotometry was used to assess the concentration of magnesium in sera and, after sample mineralization, in all the tissues investigated. For each tissue, ion concentrations were related to wet tissue mass. The results were evaluated by the Mann-Whitney test. The values of cations were as follows: serum magnesium (mmol/L): F, 0.73 +/- 0.11; M 1, 0.65 +/- 0.04; M II, 0.64 +/- 0.05; erythrocyte magnesium (mmol/l): F, 2.23 +/- 0.34; M 1, 2.25 +/- 0.23; M II, 2.25 +/- 0.19; myocardial magnesium (mmol/kg): F, 8.37 +/- 0.30; M I, 8.40 +/- 0.82; M II, 7.19 +/- 0.52). Comparison of values for magnesium concentration in the myocardium was: F vs M II, p < 0.001; M I vs M II, p < 0.001; F vs M I, non-significant. In conclusion, significant differences in myocardial magnesium concentrations among the groups and non-significant differences in sera and erythrocytes suggest that the actual concentration of intracellular magnesium, i.e. in myocardium and other tissues, cannot be derived from either serum or erythrocyte concentrations. Interestingly, in female rats there was a negative correlation between magnesium and calcium levels in the myocardium, while in both male rat groups (males I and males II) this correlation was positive.